1. Field of the Invention
The present invention relates in general to an apparatus for starting an engine and generating electricity, and more particularly to techniques relating to such an engine starting and electricity generating apparatus which is compact in construction with a reduced axial dimension thereof.
2. Discussion of the Related Art
U.S. Pat. No. 5,132,604 discloses an example of engine starting and electricity generating apparatus, which includes (a) an engine operated by combustion of a fuel and having a crankshaft, (b) a motor/generator disposed such that an axis of rotation of the motor/generator is spaced apart from and parallel to an axis of rotation of a crankshaft of the engine; (c) a planetary gear device of a single planetary type accommodated in a casing and including a carrier disposed coaxially with the engine and connected to the crankshaft, a sun gear connected to an output shaft of the motor/generator, and a ring gear, said planetary gear device operating to mechanically synthesizing and distributing forces among the carrier, sun gear and ring gear, and being arranged such that a speed of rotation of the carrier in a forward direction by operation of the engine is reduced when the sun gear is rotated in the same forward direction with the ring gear held stationary; (d) a ratchet mechanism interposed between the casing of the planetary gear device and the ring gear, and electrically controlled to inhibit the ring gear from rotating in a reverse direction opposite to the forward direction while allowing the ring gear to rotate in the forward direction; and (e) a one-way clutch interposed between the carrier and the sun gear, and operating to inhibit a speed V2 of rotation of the sun gear from being lower than a speed V1 of rotation of the carrier while allowing the speed V2 to be equal or higher than the speed V1, and wherein the motor/generator is used as an engine starter motor for starting the engine, and as an electric generator during operation of the engine.
In this engine starting and electricity generating apparatus, the single motor/generator is capable of starting the engine and generating electricity. When the engine is started, the rotating speed and torque of the motor/generator are respectively reduced and boosted by the planetary gear device, so that the boosted torque is transmitted to the engine for starting the engine. When the electricity is generated by the motor/generator, the carrier, sun gear and ring gear of the planetary gear device are rotated as a unit by the action of the one-way clutch, so as to prevent an excessively high speed of operation of the motor/generator. This apparatus may employ an inexpensive motor/generator which have relatively small mechanical and electrical capacities.
In the known engine starting and electricity generating apparatus as described above, the planetary gear device is disposed coaxially with the engine, whereby the apparatus tends to have a relatively large dimension in the axial direction of the engine. In a front-engine front-drive automotive vehicle, the engine is installed with its axis extending in the transverse direction of the vehicle. Therefore, it is not easy to dispose the planetary gear device coaxially with the engine, in the front-engine front-drive vehicle. Further, the one-way clutch interposed between the sun gear and the carrier of the planetary gear device is required to have a comparatively large torque capacity and an accordingly large size. This requirement increases the axial dimension of the engine starting and electricity generating apparatus, making it more difficult to install the apparatus on the front-engine front-drive vehicle.